Automotive steering systems incorporate a steering wheel for operation through a driver, said steering wheel introducing the steering torque applied to an axle with a steerable wheel through a steering column and a gear. In an effort to reduce the steering wheel forces required by a driver upon steering when the vehicle is standing still, during manoeuvring or at low driving speeds, many vehicles have steering assistance, which is referred to as power assisted steering.
Manual, hydraulic, electro-hydraulic but also increasingly electromechanical steering systems are being utilized in vehicles. Through direct intervention in the respective electronics and data processing of the vehicle, the force required to affect steering (also referred to as “steering feel”) can be adapted to the corresponding type of vehicle and the respective driving situation. The torque applied by the driver to the steering system remains the elementary variable when seeking a desired steering feel and must be measured when incorporating power assisted steering. Irrespective of the physical principle of steering assistance, actual assistance via a power assisted mechanism depends on the applied torque if one desires to acquire a realistic driving feel.
If in hydraulic steering the amount of assistance is provided by the mechanically operated rotary slide valve, conversion of the torque into an electrical signal is always needed in case of assistance through an electric actuator.
Examples for such electromechanically assisting steering systems are:                Single-/double pinion Electromechanic Power Assisted Steering (EPAS);        Centric-/concentric rack EPAS; and        Column EPAS.        
Electromechanical steering systems mainly find application in subcompact or mid-size cars because the power provided by the 12V onboard power system is limited. Accordingly, vehicles capable of bearing a high axle load cannot operate or are difficult to operate with such electromechanical steering systems. For this reason, work is presently accomplished on systems relying on hydraulic operation in which the steering valve is replaced by an electrically-operated valve. As a result, vehicles capable of bearing high axle loads can be handled without having to obviate the EPAS typical functionalities. It will be understood that such power steering mechanisms require that the torque applied by the driver must be converted into an electrical signal. Examples thereof are:                Electronic valve System (or “E-valve”)        Closed-center System        
Irrespective of the physical principle of the respective steering assistance, the steering torque serves as a measurement value in generating appropriate steering assistance provided to the driver of the vehicle, wherein the assistance is provided by an actuator such as an electric motor. Accordingly, it is necessary to determine or measure the torque applied by the driver of the vehicle and then convert the measurement of the torque into an electrical signal. Those skilled in the art presently know of different torque sensors by means of which the respective generated steering torque can be detected.
They include for example:                Magnetoelastic sensors making use of the effect that the resistance changes when the magnetic field changes;        Inductive sensors which rely on the physical laws of electromagnetism but do not have two or more coils like above but only one coil;        Hall effect sensors using the Hall effect for measuring magnetic fields and currents for location; or        Potentiometric sensors which are passive sensors that rely on a potentiometer and with the help of which the physical variables of length and angle show themselves as analogue electric variables like voltage or current.        
Unfortunately, and as a disadvantage, known systems require and rely upon a torsion rod having a predetermined rigidity through the angle of rotation such that the applied steering torque (e.g., a hydraulically operated steering mechanism), is detected and converted into an electrical signal. Such a torsion rod is designed to have a defined rigidity so that the angle of rotation thereof constitutes an admeasurement of the applied torque. The principles described herein above rely upon the measurement of the applied torque (as provided by the relative rotation of the torsion rod) to accomplish conversion of the measurement into an electrical signal. In addition thereto, integration of the torsion rod in the steering assembly represents additional expense in terms of design and production.
It is also known to use strain gauges to determine torques. The basic principle of a strain gauge is based on a change in the electrical resistance of a conductor. Specifically, the electrical resistance of a measurement grid located in the sensor changes upon deformation in the direction of measurement. The cause of the deformation may for example occur through a change in force, pressure or torque. In the current methods of manufacturing strain gauges, a conductive pattern is etched out of a metal foil that is applied onto a carrier film. Then, this carrier film is applied by means of special glue onto the component part of the steering mechanism to be monitored. The manufacture and attachment of the strain gauge are complicated and often cause problems. This is in particular the case if the component part to be monitored is made from an electrically conductive material. In particular, an electrically isolating layer must be provided between the strain gauge and the electrically conductive item (i.e., component part) to be inspected.